This invention relates to a screw-nut screw coupling of the type comprising a first and second element coupled together in such a manner that rotary motion of one of them produces corresponding translatory motion of the other.
In particular the present invention relates to a screw-nut screw coupling of the type comprising a tubular element with at least one internal helical groove of constant pitch; an elongated element extending with radial slack through said tubular element and comprising externally at least one helical groove of pitch substantially equal to the pitch of said internal groove and defining with this latter a first rolling path for a plurality of balls interposed between said elongated and tubular elements, and recirculation means defining at least one second rolling path of said balls and extending between two distinct points of said first path and parallel thereto, to define with this latter an endless rolling path for said balls.
In known screw-nut screw couplings of the type heretofore described, the said tubular element generally consists of a single piece normally produced by mechanical chip-forming machining starting from a block of special steel, on which one or more external ducts are added when machining is finished, each duct defining a recirculation path for said balls. Because of the relatively high costs of such a manufacturing process, the use of screw-nut screw couplings of the aforementioned type has been substantially limited to extremely sophisticated applications in which the need to obtain maximum operational precision and minimum friction outweighs any cost consideration.